U.S. Pat. No. 4,572,226 describes a push button automatic open and close umbrella that operates by a drive motor and a drive mechanism and has a manual override device. The umbrella's drive mechanism operates by means of a motor which drives rods to rotate a drum along a stationary threaded split shaft to operate a runner. Its manual override device incorporates two spring biased arms each having a contact member to compress the stationary threaded split shaft to disengage the threads of the split shaft from the drum. However, the split shaft design is difficult to manufacture and can yield during operation in high wind conditions, for example. Thus, a major disadvantage of this design is that the repeated coupling and uncoupling of the split shaft threads from threads of the driven member which supports the canopy of the umbrella will tend, in time, to cause excessive wear of the threads with consequent slippage, further wear and eventual breakdown. Accordingly, there is a need for a drive mechanism that is relatively easy to manufacture and is more durable than the split shaft design heretofore described.